1. Field of the Invention
The present invention relates to a field-effect transistor such as -a thin-film transistor and to a manufacturing method therefor. Further, the present invention relates to a manufacturing method for a display device using the field-effect transistors and to a display device manufactured using the manufacturing method for the display device. More specifically, the present invention relates to a field-effect transistor such as a thin-film transistor having a gate electrode, a source electrode, and a drain electrode of the thin-film transistor simultaneously formed by patterning a same starting film by use of photolithography and to a manufacturing method therefor.
2. Description of the Related Art
Hereinbelow, an example of a conventional manufacturing procedure for a thin-film transistor will be described. An amorphous silicon film is formed on the upper side of a glass substrate, the amorphous silicon film is crystallized, and a crystalline silicon film is thereby formed. Then, the crystalline silicon film is patterned into an island-like crystalline silicon film, and a gate insulation film is formed on the island-like crystalline silicon film. Subsequently, a conductive film formed on the gate insulation film is patterned, and a gate electrode is thereby formed. Then, using the gate electrode as a mask, an impurity is introduced to the island-like crystalline silicon film by using an ion doping method, and a source region and a drain region are thereby formed. Next, a first interlayer insulation film is formed on both the gate electrode and the island-like crystalline silicon film. Then, an opening (contact hole) is formed by performing patterning on the first interlayer insulation film so as to reach the source region and the drain region. Thereafter, a conductive film to be connected to the source region and the drain region is formed, and the conductive film is then patterned. Thereby, a source electrode and a drain electrode are formed. The thin-film transistor is manufactured according to the above-described procedure. The aforementioned procedure is well known (Refer to, for example, a patent document 1 below). When applying the thin-film transistor manufactured according to the well-known art to a pixel portion of a display device, a second interlayer insulation film is formed on both the source electrode and the drain electrode, and an opening is formed by performing patterning so as to reach one of the source electrode and the source electrode. In addition, a transparent conductive film is formed and patterned, and a pixel electrode is then formed.
(Patent Document 1)
Japanese Patent Application Laid-open No. Hei 8-330602 (FIGS. 1A to 1F; First Embodiment)
As described above, according to the conventional procedure, the source electrode and the drain electrode are formed after the gate electrode has been formed. That is, ordinarily, formation of the gate electrode and formation of the source electrode and the drain electrode are separately performed. Therefore, in the processes progressed to the stage where the formation of the source electrode and the drain electrode is completed, four patterning steps are performed, and four photomasks are used in the patterning steps. To complete the formation of the pixel electrode, two more patterning steps are performed. That is, in the above case, the number of the patterning steps is six, and the number of the photomasks used in the patterning steps is accordingly six.
At present, improvements in the throughput (quantity that can be processed in a unit time) and the yield (ratio of the number of finished products to the number of inputs to a manufacturing line) are strongly demanded in the field of the manufacture of field-effect transistors such as thin-film transistors and display devices using the field-effect transistors.
However, in the conventional procedure, since the number of steps in the conventional procedure is large, the time required for the manufacture of field-effect transistors and display devices cannot easily be reduced, and it is difficult to improve the yield. For example, because of shrinkage of a substrate or for other causes, a positional offset of a fine pattern formed in a subsequent patterning step can unexpectedly occur. The positional offset of the pattern results in the manufacture of defective products as well as in reduction in the yield. For example, in a step of forming an opening (contact hole) by performing patterning to form the source electrode and the drain electrode, the position of the opening is offset from the source region and the drain region where the opening is intended to be provided.
A case can be in which even when a positional offset of a pattern is caused at one patterning step, the offset is as slight as that falling within an allowable tolerance, and no adverse effects are thereby caused on the operation of a finished display device. However, when a number of patterning steps are repeatedly performed, the slight positional offset is enlarged, thereby increasing the probability of defective-product occurrence.